I don't have one so can't say for sure. But having spoken to people who do, they are pretty strong but are easily defeated in pvp because anyone wearing a fire guard will take 0 damage from it.
I'm sure some people who actually have dragons will be on here soon enough to give you better facts.
However 1 thing I would say, is anything you plan to use a dragon evo stone on, get your money's worth by making sure it's fed up accurately. Decide what stat you want and focus on that entirely, so you make it as good as it possibly can be. I'd expect INT would be the one to go for in this case.